Fig. 4.

Morphology of cells in NL during secondary morphogenesis. At E13, Golgi material revealed the presence of neuroblast-like cells in the rostral ends of the cochlear anlage. ByE17, when NL exhibited a laminar structure, NL cells began to exhibit dendritic polarization, with most of their dendrites projecting within the dorsoventral axis. By E23 in central NL, when the separation of the NL cells away from the lamina had begun, two distinct cell morphologies were observed. In the regions where the cells are confined to the middle of NL in a laminar structure, NL cells were clearly polarized with two dendritic tufts projecting dorsally and ventrally (left panel). In contrast, and on the same section, where NL has undergone the loss of the laminar organization, NL cells show dendrites distributed around their cell bodies and no obvious polarization (right panel). The morphology of the bitufted cells was reminiscent of the shape of the cells in NL in chickens, emus, and crocodilians, whereas the morphology of the cells after the loss of the laminar organization resembled that of the adult owl. NL cells continue to mature, and E31 neurons exhibit many short, fine dendrites (Carr and Boudreau, 1996). Scale bar, 20 mm.